1. Field of the Invention
The present invention relates to a manufacturing method for a double-sided wiring board and, more particularly, to a technique for fabricating double-sided boards having at least a first access opening extending therethrough whereby circuit components on one side of such a board may be connected to a wiring pattern on the other side of the board.
2. Description of the Related Art
Double-sided circuit boards, i.e., electrical circuits with wiring patterns formed on the opposite surfaces of a resinous insulating layer, are well known and have many uses. In the use of such a double-sided circuit board, it is often necessary to provide access through the board from one side to the circuitry on the other side. Conventional methods of forming an access opening or through-hole in a double-sided circuit board, such an opening being used for example to connect a circuit component to a wiring pattern on at least one surface of the board, include laser machining, chemical etching and mechanical pre-punching of the insulating layer of the board.
The prepunching technique, however, requires that an opening be made beforehand by a punching means or the like in a predetermined position of an insulating layer and that the opening then be filled with a filler which can be removed in a later process. The filling of the punched opening is in the interest of facilitating the production of the wiring patterns. In addition, accurate alignment with the opening is required when producing the wiring patterns on both surfaces. These requirements lead to an extremely complicated process, placing various restrictions in manufacturing very fine, double-sided, flexible circuit boards.
As a technique for mass production, laser machining poses many problems, including high equipment cost, frequent maintenance required for maintaining optimum laser conditions at all times to ensure the best suited conditions for micromachining a resinous insulating layer, high operating cost for laser equipment, and the potential change in the insulating characteristic of the resinous insulating layer due to electrically conductive carbides which are liable to be formed at a laser machined section.
In the case of resin etching by chemical means, many resinous etchants contain materials which are extremely harmful to human bodies; therefore, a considerable amount of equipment cost is required to build a stable and safe manufacturing line wherein careful consideration is given to operation, maintenance, management, the disposal of waste liquids, etc.